The aging U.S. population has led to substantial increases in resources allocated to the prevention and treatment of age-related neurodegenerative conditions, including disorders of cognitive decline. Alterations in homeostatic functions such as energy balance and sleep patterns are also frequently seen in the elderly and these changes often precede and predict subsequent cognitive decline. A novel hypothesis is that some of these seemingly disparate manifestations of age-related deficits may share underlying neurobiological mechanisms; that is, brain regions that are involved in homeostasis regulate the activity of neurotransmitter systems and brain regions that mediate the appropriate behavioral and cognitive responses to physiological challenges, and these interactions may be impacted in aging. We have shown that aging is associated with loss of hypothalamic hypocretin/orexin neurons-a cell population that regulates energy balance and sleep/wake stability. Because hypocretin/orexin neurons also regulate neurotransmission in brain regions that underlie several aspects of attention, learning and memory we hypothesize that these neuropeptides link physiological function with age-related cognitive decline. The testable corollary to this hypothesis is that upregulation of the orexin/hypocretin system in aging will allow for preservation or restoration of these functions. In Aim 1 we will combine DREADD (designer receptors exclusively activated by designer drugs) and in vivo neurochemical approaches to determine the effect of acute orexin/hypocretin activation or inhibition on behavior and neurotransmission in several relevant brain regions. In Aim 2 we will use virus-mediated gene transfer and to perform chronic manipulations of the orexin/hypocretin system in a longitudinal animal model of aging. We will examine how these manipulations alter food and water intake, body composition and markers of neurotransmitter systems and neuronal activation. In Aim 3 we will test the hypothesis that the hypocretin/orexin system supports attentional performance across the life span using both acute and chronic manipulations of hypocretin/orexin transmission. Collectively, these studies will implicate the orexin/hypocretin system as a major contributing factor in cognitive and homeostatic manifestations of age-related neural dysfunction, and suggest a potential new target for development of therapies that prevent, delay or ameliorate age-related cognitive decline.